In conventional wideband, high density magnetic signal processing, magnetic flux transferred to or from a magnetic storage medium permeates a magnetic core of a magnetic transducer (i.e., a head). During reproduction operation modes this flux produces an induced output voltage which, after suitable amplification, is a reproduced representation of the magnetic flux from the media that permeates the core and is suitable for use by a utilization device. During record operation modes, the permeating flux results from current applied to the transducer coil winding, and the flux fringes from a physical gap provided in the core for recording a representative signal in the magnetic storage medium.
One problem with prior art magnetic storage systems is that various losses occur during signal transfers between the magnetic storage medium and the transducer. One of the more significant losses, called "spacing loss", results from the physical spacing between the magnetic storage medium and the transducer. Spacing loss is particularly deleterious during reproduction operations where the effects of such loss are more significant. Prior efforts to reduce spacing loss primarily involved reducing the physical spacing by placing the transducer as close to the magnetic storage medium surface as operating conditions permitted. Such positioning, however, is accompanied by an increase in the likelihood of collisions between the transducer and magnetic storage medium, particularly in devices in which the transducer is normally supported above and out of contact with the storage medium surface, i.e., the transducer "flies" relative to the storage medium. On the other hand, if the transducer is in physical contact with the medium, damaging wear occurs due to the contact. However, it should be noted that if contact heads are used, the head is still separated from the storage medium by the carbon overcoat that is standard in such disks.
In addition to spacing loss, signal quality is also adversely affected by poor efficiency in signal transfer to and from the transducer. Reproduce gap loss is an example of one of the causes of poor efficiency. Reproduce gap loss is caused by the finite length of the physical gap within the transducer that is responsible for effecting signal transfers between the transducer and medium, and is manifested by a loss of output signal at shorter wavelengths. Reproduce gap loss is generally considered to be an inherent result of transducer geometry.
U.S. Pat. No. 5,041,922 to Wood et al (hereinafter "Wood et al."), assigned to the assignee of the present invention, discloses a magnetic recording system which includes a magnetic medium having an overlying or underlying "keeper" layer of magnetically saturable high permeability material. As disclosed in Wood et al., the properties of the keeper layer are selected to act as an extension of the head poles, thereby effectively bringing the head closer to the magnetic medium and reducing the spacing loss. Since one of the material properties of the head poles is high permeability, the keeper layer material in Wood et al was also selected to have high permeability. Since permeability of a material is generally a function of its thickness in thin film devices, if high permeability is to be attained, it requires a relatively thick keeper layer.
Use of a thick keeper layer may increase record losses. In general, the record losses increase as the thickness of the magnetically saturable layer overlying the medium increases. This is primarily because of attenuation of the write flux from the transducer, since it has to penetrate the overlying keeper layer in order to reach the magnetic storage layer in which data is being recorded. Therefore, although the high permeability keeper layer disclosed in Wood et al improves the system signal-to-noise ratio during reproduce operations, it may increase record losses due to the keeper layer thickness required to achieve high permeability, and thereby reduce the net gains.
Additional problems with prior art magnetic storage systems result from their widespread use of inductive heads (ferrite or thin film). As densities of disks increase, the number of coils (i.e., turns) in the head must also be increased in order to detect the weaker flux signals associated with the transitions of the denser disk. However, this increases the inductance of the head to an unacceptable level which may create a system resonance with the capacitance of the reproduce amplifier, and thus interfere with the reproduction of data stored on the magnetic storage medium.
Increased head inductance also creates problems during the write cycle. The larger the inductance of the head, the more time it takes for current to build up through the winding before sufficient flux is available at the tip region to write to the disk. Hence, a designer has to select a write speed sufficiently slow to ensure that the disk operates within acceptable criteria, or the designer has to provide a larger drive circuit to drive the head hard enough (i.e., increase the applied voltage) to overcome the high inductance.
A further problem with inductive heads is that as the density of the magnetic storage medium increases, the noise created by the head also increases, This, in turn, decreases the system signal to noise performance that can be attained from a magnetic storage system employing an inductive head, and eventually limits the recording density.
Hence, there is a need for a magnetic storage medium and system with improved storage capacity. In addition, there is a need for a magnetic storage system with an improved system signal to noise ratio during record mode operations, that also reduces record losses.